Indeed, the right playing time for any game is when it ends before getting boring!
Quotes about long games
I’m not of the school that a game should be short by principle. I like a deep game, I like a multi-layered game. As a player, if I play a game and crack it, get it from the get go, I’m probably not interested in playing it again. And that’s not what I want to offer to people who buy my games.